Sonic atomizer for liquids



Dec. 11, 1962 R. J. LANG ET AL somo ATOMIZER FOR LIQUIns Filed Oct. 27,1960 Potent Attorney Dec. 11, 1962 R. J. LANG ET AI 3,067,948

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Robert J. Lon

g Inventors Jerrold D. AIIos By Paten A torney Dec. 1l, 1962 R. J. LANGET AI. 3,067,948

SONIC ATOMIZEIR FOR LIQUIDS Filed Oct. 27, 1960 4 5119615-31991@ 5 .'rolI I 36 .sow so g FoRcEIo 2a LLI LLI II E 20- IO E TRANsoucERPowER=coNsTANT D TRANsDucER FREQuENcY=2oKcPs 8 E TRANsDucER TIPoIA.=o.437 IN. 6

.Io TRANsDucER TIP To ORIFICE 2 O6 PLATE nIsTANcEHaooIN. 4 .o2 2 o l I II I .OIO .Q20 .030 .O40 .O50 .O60 .O70 ORIFICE OPENING DIAMETER-INCHESFig. 4

20o I I Iso n 0.275 GPH Iso AToMIzED LIQUID: WATER TRANsDucER PREQuENcY=2o KcPs |4O TRANsDucI-:R TIP DIA.=o.4s? IN.

TRANSDUCERA TIP TO ORIFICE |20 PLATE DISTANCE `0.00 IN.

l ORIFICE OPENING DIA. 0.040 IN.

MASS MEDIAN PARTICLE DIAMETER-MICRONS 0 I I I I I I 200 220 240 260 280300 320 340 360 380 APPARENT AIR vsLocITY THROUGH oRIPIcE oPENING-PEET/sEcoNn Fig. 5

RobeI'I` J. Long Jerrold D. Anus lnvenwrs Bym w A7, Potent t rney Dec.1l, 1962 R. J. LANG ErAL soNIc AToMIzER FOR LIQUIDs 4 Sheets-Sheet 4Filed-Oct. 27, 1960 Inventors Robert J. Long Jerrold D. Atlas By fwn/MPotent Attorney Vpiece is in the form of a cylinder.

United States Patent Of ce 3,067,948 Patented Dec. 11, 1962 3,067,948SONIC ATOMIZER FOR LIQUIDS Robert J. Lang, Watchung, and Jerrold D.Atlas, Plainield, NJ., assignors to Esso Research and EngineeringCompany, a corporation of Delaware Filed Uct. 27, 1960, Ser. No. 65,5376 Claims. (Cl. 239-4) This invention relates to a method and apparatusfor atomizing liquids. It relates particularly to a method and apparatusfor atomizing liquids through the use of sonic energy, and it relatesmore particularly to such a method and apparatus wherein and wherebysonic energy is used for the production of a rapidly pulsating stream ofair to impinge upon the liquid to be atomized.

It is well known in the art that atomization of liquids may be eifectedthrough the use of sonic energy. A pertinent reference is the articleUltrasonic Atomization of Liquids by J. N. Antonevich appearing at pp.6-15 of Transactions on Ultrasonics, February 1959, published by theInstitute of Radio Engineers. One apparatus which has been used foratomizing liquids is a transducer compr-ising a piece of ceramicpiezo-electric material such as barium titanate bonded on a flat surfaceto the larger diametral surface of a truncated conical resonator ofelastic and electrically conductive material such as aluminum. rln aparticular apparatus of the prior art, the ceramic The length of thiscylinder and the resonator to which it is bonded are respectivelyone-half the wavelength of sound in their particular materials at theoperating frequency selected. Such apparatus is illustrated anddescribed, for example, in U.S. Patent No. 2,514,080 to W. P. Mason,issued .luly 4, 1950. i

When an alternating voltage of relatively high frequency is appliedacross the ceramic cylinder, this cylinder will be cyclically lengthenedand shortened and Iwill gene-rate alternate compression and rarefactionwaves of sonic `energy. This energy, which may be characterized by a-frequency above the range of normal hearing, will cause a cyclicallengthening and shortening or longitudinal vibration of the metalresonator as it ilows thereinto. With -decreasing cross sectional areaof a cone-shaped resonator in the direction away from the ceramiccylinder, there will. be a concentration of energy near the resonatortip and an increasing amplitude of motion. If a drop of liquid such ashome heating oil be applied to the resonator Atip while the resonator isbeing vibrated longitudinally, sonic energy will flow into this drop andthel drop will -be broken up into a fog of fine particles; that is, itwill be atomized.

Like this equipment and process of the prior art, the present inventionprovides an atomizing apparatus and `method wherein and whereby a sonicenergy transducer is employed. Unlike the prior art equipment andprocess, however, the sonic energy transducer of this invention does nothave the liquid to be atomized applied directly onto it. Instead,according to this invention, the tip of the resonator element of thetransducer employed is disposed in closely spaced relation to theopening in an orifice plate, and liquid to be atomized is trickledacross this plate toward the opening therein on the side of the plateaway from the transducer. When the transducer is energized, it acts as apump or blower to draw air in through the orice opening in a wide-anglepattern on the retracting or suction stroke of the resonator element tipand then discharge air from this same opening in a narrow, jet-likestream on the subsequent forward or driving stroke. Liquid running overthe edge of the orifice opening is impinged upon by this stream, andconsequently atomized.

The nature and substance of this invention will be more clearlyperceived and fully understood by referring to the following descriptionand claims taken in connection with the accompanying drawings in which:

FIG. l represents a side elevation view partly in section of a highfrequency electronic generator coupled to a sonic energy transducerdisposed horizontally in a suitable mounting, an orifice plate beingprovided closely adjacent the tip end of the resonator element of thistransducer according tothe present invention, and this plate havingmounting means whereby its position relative to the transducer may beadjusted;

FIG. 2 represents a plot of particle size distribution obtained using anapparatus embodiment of this inlvention for the atomization of moltenwax;

FIG. 3 represents a plot of force and velocity of an air jet generatedby an apparatus embodiment of vthis invention measured with respect todis-tance from the tip of the resonator element of the sonic energytransducer to the orifice plate for given Values of resonator elementtip diameter and orice diameter;

FIG. 4 represents a plot of force and velocity of an air jet generatedby an apparatus embodiment of this invention measured with respect toorice diameter -for given values of resonator element tip area anddistance from the tip of the resonator element to the orifice plate;

FIG. 5 represents a plot of mass median drop diameters obtained using anapparatus embodiment of this invention for the atomization of watermeasured with respect to apparent air velocity through the orifice for aplurality of rates of liquid feed; A

FIG. 6 represents a side elevation view partlyy in section of the tipend of the resonator element of the vsonic energy transducer of FIG. land an orifice plate closely adjacent thereto, this plate being providedwith a plurality of oriiices, and y f FIG. 7 represents a side elevationView partly in section of the tip end of the resonator element of thevsonic energy transducer of FIG. 1 disposed vertically'and an orificeplate closely adjacent thereto.

Referring now to the drawings in detail, especially 'to FIG. l thereof,a high frequency electronic generator Vor oscillator 10 havingconnection to a low frequency vvoltage source through cable 12 and plug14 is closely coupled on its output side by means of cable 116 acrossthe bore of a cylindrical-type piezo-electric element 1-8 of a sonicenergy transducer 20. This piezo-electric element is bonded to a boss onthe larger diametral surfaceof a resonator element 22 of generallyconical form.y At its smaller diametral surface, the resonator elementis drilled and tapped to receive the shank of a headed bolt 24. The

diameter of the head of this bolt is effectively the diameter of the tipend of the resonator element for purposes of the present invention.Accordingly by having available a plurality of bolts 24 of differenthead diameters, a range of tip sizes of the resonator element may beobtained by substitution of bolts one for another.

For purposes of the present invention, it is notcritical that generator10 be of the electronic variety.v This generator may be of the rotaryvariety also, both varieties and their uses being well known in thesonic energy art. Likewise, the nature of piezofelectric element 18 isnot critical. This element may comprise any one'of several materials.Use in ysonic energy transducers off-'such a piezo-electric material asthe ceramic barium titanate has been mentioned already. Other ceramicmaterials suitable for this use include lead zirconatesv and leadzirconium titanates. In assembling transducer 20,tl|1e electrical leadsor lugs of piezo-electric element 18 are soldered thereto, and thenthisY element is bonded* to resonator element 22. 'Ihe bond betweenthese two 'elements is critical for proper operation of the transducer,although neither its structure nor the method of making it constitutesany part of the present invention. In one suitable method of joining thepiezo-electric and resonator elements, a cement such as an epoxy resinis used which sets by polymerization rather than by solvent evaporation.A suitable elastic and electrically conductive material for theresonator element is aluminum, as mentioned above. Other materialsappropriate for resonator element 22 include brass and stainless steel.

In the apparatus embodiment of this invention illus- .trated in FIG. 1,support for transducer 20 is furnished from base element 26. Anupwardly-extending post member 28 is threaded into a raised region 30 ofbase 26, and locked in place with nut 32. At its upper end, thisvertical member has a transducer locating ring element 34 threadedthereonto and locked with a nut 36. This ring element encloses resonatorelement 22. The resonator is maintained in spaced relation to ring 34 bymeans of three point-ended screws 38 substantially equally spaced aroundthe ring element, and having lock nuts 40. These screws directedradially inwardly through ring 34 engage notches or drill spots in thelateral sur face of the resonator element. All these spots should be ina single circumferential line on this element, and this line shouldcoincide with the node of vibrations in the resonator when transducer 20is energized from generator 10.

Closely adjacent the head end of bolt 24 there is an orifice plate `42.While this plate may actually be in contact with the bolt head at leastintermittently during operation of transducer 20, no physical bondexists between the plate and the bolt. Plate 42 may conveniently be ofcircular form, but it is not required to be so configured. In its centerit is provided with a lipped orifice opening 44 in substantially axialalignment with transducer 20, thc lip or rim of this opening extendingaway from the transducer. At its outer edge region, plate 42 is slightlyupset to fit closely over and extend outwardly along a shaped annularsurface of frame member 46. The plate is held tightly on and againstframe 46 by means of a clamping ring 48, whereinto are threaded aplurality of thumb screws 150 which pass through clear holes in frame46. There are likewise holes or slots in the outer edge region oforifice plate 42 for accommodation of the thumb screws.

Extending across the lower region of frame 46 and fixedlysecured theretoby a plurality of screws 52 is a rigid yoke member 54. This yoke isbored vertically to have at least one clear hole through which passesthe upper threaded end of a post member 56. Yoke 54 is secured on post56 by means of nuts 58 and 60. The

lower end of post 56 is threaded into a sliding block rnembier 62, andis locked therein by means of nut 64. Block 62 is characterized by aguide element 66 formed on or fitted onto its lower surface. This guideelement, which .may be wedge-shaped in transverse section, fits closelyinto a groove region 68 formed in base 26. Block 62,

. guided by element 66 running in groove 68, may slide on surface 70 ofbase 26. This surface will preferably be smoothly finished as 'will bethe surface of block 62 ,sliding upon it, and also the bearing surfacesof guide element 66 and groove region 68.

At least one position-adjusting rod 72 is threaded into block 62, andsecured therein by means of nut 74. This rod, threaded at both ends,extends horizontally through `a clear hole in raised region 30 of base26. On its threaded end extending to the left beyond raised base region30, rod 72 is provided with two wing nuts 76 and 78, the first of thesebeing intended to bear against a lateral, preferably finished surface 80of raised base region 30, and the second being intended to bear and lockagainst the first. A compression spring 82 encloses adjusting rod 72,and is contained between sliding block v'62 and raised base region 30.The force of spring 82 acting against block 62 tends to move this blockin a direction carrying orifice plate 42 away from the tip end oftransducer 20.

The remaining structural item appearing in FIG. l is feed tube S4through which liquid to be atomized is flowed onto plate 42. This tubehas connections not shown leading to a source of liquid, a tank of homeheating oil for example, these connections including appropriate pumpingand metering devices. The mounting of feed tube 84 will be capable ofmovement so that this tube may be moved not only simultaneously 'withthe orifice plate as sliding block 62 is shifted, but also, desirably,independently of plate 42 to allow adjustment of the position of thetube outlet end with respect to orifice opening 44. `In general, thisoutlet end should be so positioned that liquid will flow from it acrossthe plate to the lipped region thereof surrounding the orifice opening.

Although the machine elements which would be involved are notspecifically illustrated, it is obviously within the scope of well knownart that means for recovering liquid material flowed onto but notatomized from plate 42 could be provided. Such means might include, forexample, a drip pan located below the plate and a scraper operatingacross the face of the plate removed from transducer 20.

Adjustment and operation of the apparatus shown in FIG. 1 will now beconsidered. Locking wing nut 78 is backed off from adjusting wing nut76, and the latter nut is manipulated to shift sliding block 62 asnecessary to offset plate 42 from the head of bolt 24 by a distancesubstantially equal to half of the total displacement of the tip of theresonator element, that is, effectively, the displacement from staticposition of the bolt on its forward stroke upon transducer 20 beingenergized from generator 10 to vibrate longitudinally. Wing nut 78 isthen tightened against wing nut 76. Nuts 58 and 60 may be manipulated toshift yoke 54 up or down on post 56, and so adjust the position of plate42 to center orifice opening 44 vertically with respect to transducer20. Although no means of making transverse adjustment of the orificeplate position are particularly illustrated, it is obvious that suchmeans could be provided easily if desired. However, if no such means areprovided, satisfactory results will be achieved within the scope ofother adjustments if the illustrated parts are so designed that orificeopening 44 is centered transversely with respect to the head of bolt 24.Such centering is indeed practically required.

Orifice plate 42 having been positioned with respect to transducer 20,`liquid feed tube 84 is positioned with respect to this plate. The nextstep is to start generator 10 according to procedures appropriate tothat piece of equipment. Such procedures do not constitute` any part ofthe present invention. With generator 10 imposing a high frequencyalternating voltage, about 2O kc. p.s., for example, across oppositeside walls of piezo-electric element 18 there will be a cyclicalincrease and decrease in diameter of this element. Due to well knownelastic effects, this variation in diameter will cause a cyclical changein length of the piezo-electric element. This high frequency lengtheningand shortening of piezo-electric element 18 will cause a flow of sonicener'gy into resonator element 22. Physically, this ow will be evidencedby a high frequency lengthening and shortening of the resonator element.Actual movement of any region of this element or part effectively aportion thereof will be greatest at the head of bolt 24 adjacent orificeplate 42.

As the head of bolt 24 advances toward and withdraws from orifice plate42 it acts, in effect, like the piston of an air pump. Without specificlimitation to any particular theory, the pumping action which isobtained is considered to be substantially the same as that described inU.S.

`Patent No. 2,787,444 of April 2, 1957, issued to C. W.

Skarstrom for Heat Exchanger and Means for Circulating Fluids. Insummary, as the head of bolt 24 withdraws from orifice plate 4Z there isinward or leftward ow of air through orifice opening 44 from anextensive area over the outer or right hand surface of the orifice platewith the flow lines Widely dispersed in a large solid angle. This isindicated in FIG. 1 by sinuous arrows. Thereafter, as the head of bolt24 advances toward the orifice plate, air is discharged to the rightthrough the orifice opening in the form of a jet or stream of smallsolid angle. This is indicated in FIG. 1 by straight dashed arrows. Thejet of discharged air in turn induces fiow of -air from the surroundingatmosphere as indicated by curved dashed arrows.

After transducer 20 has been energized to start the pumping action justdescribed, flow of liquid to be atomized may be started through feedtube 84. This liquid will run down the orifice plate and onto the lippedregion thereof surrounding and defining the orifice opening. AS theliquid feed goes over the edge of the lipped region of orifice plate 42it will be struck by the pulsating jet of air issuing from orificeopening 44, and will be broken up into fine particles or atomizedthereby. The air jet will not only atomize the liquid feed, but willalso give it an appreciable displacement to the right away from theoriiice plate. Said in other words, a jet of air and atomized liquidwill issue from orifice opening 44. This stream is indicated in part bythe particle fog S6. Air fiowing according to the curved arrows in FIG.1 will tend to be drawn into this mixture stream, and may be helpful informing a combustible mixture when the atomized liquid is heating oilfed at a relatively high rate.

Referring next to FIG. 2, experimental measurements have been made ofthe diametral size distribution of liquid particles generated by anapparatus embodiment of this invention generally similar to that shownin FIG. l. In this embodiment the transducer had a tip diameter of about0.4 in., a tip displacement of about 0.001 in., and an operatingfrequency of about 20 kc. p.s. The opening in the orifice plate had adiameter of about 0.030 in., and liquid to be atomized was fed at a rateof about 0.01 to 0.02 gal/hr. This liquid was molten Acrawax C made byGlyco Products Co., Inc., New York, N.Y. Acrawax C is a syntheticmaterial having an unusually high and well defined melting range of284-290" F. The specific gravity of this wax in the temperature range ofS-350 F. referred to water at 60 F., and its surface tension in thissame temperature range are quite close to those of a typical home'heating oil -at 100 F., the approximate temperature at which an oil ofthis kind is'frequently atomized by traditional means such as a pressurenozzle for mixing -with air and subsequent combustion.

In the carrying out of the experiments, molten wax particles dischargedfrom the orifice opening with the pulsating air jet were cooled andcondensed, and the solidifiedk particles collected and thereafteranalyzed in a Sharples Micromerograph for distribution of size in termsof weight percentage of the whole less than any particular diameter. Theresults of this analysis are plotted in FIG.

'2. Mass median particle size was determined to be 34 microns. Thepulsating nature of the air jet whereby the molten wax was atomizedwas'found to be definitely advantageous for the generation of fineparticles. This was f shown by a second experiment in which liquid wasatomized by an air stream from a steady source of compressed air, thisstream issuing through the'opening in .the same orifice plate used withthe transducer in the irst experivment, and having axial momentumessentially the same Referring next to FIGS. 3 and 4, experimentalmeasurements have been made of the force and velocity of an air jetgenerated by an apparatus embodiment of this invention generally similarto that shown in FIG. 1. In each case the transducer had a tip diameterof about 0.437 in., an operating frequency of about 20 kc. p.s., and anessentially constant power input. For the experiments providing the dataof FIG. 4, however, the power level was somewhat higher than for thoseproviding the data of FIG. 3. Force of the jet was measured by orientingthe transducer vertically and causing the pulsating air stream issuingthrough the orifice opening to impinge upon one pan of a laboratorybalance. The weight needed to be applied to the balance to maintain itin an equilibrium position gave a direct reading of jet force. Velocityof the air jet was measured with a hot wire anemometer. 'I'he velocityValues indicated in FIGS. 3 and 4 represent profile maxima or peaksmeasured transversely across the air stream at a determined distance outfrom the orifice opening. They are essentially steady values, nosignificant cyclical variation of jet velocity on account of transducertip movement having been detectable with the instrument system used.

For the particular experiments providing the data of FIG. 3, thediameter of the orifice opening was kept at a single value of about0.040 in. Force and velocity measurernents lwere taken for a range ofstatic distances from the transducer tip, that is, the effective tip ofthe resonator element, to the orifice plate. The word static hererelates to distances determined when the transducer was in a deenergizedor non-vibrating condition. All distance values indicated in FIG. 3 arestatic, except for the zero value which represents the dynamic conditionof the transducer vibrating and so positioned that the effective tip ofits resonator element just barely touches the orifice plate on itsforward stroke. Such a zero -Value for dynamic conditions corresponds toa distance on the order of less than 0.001 in. for static conditions, avalue so small as to be not easily distinguishable from an actual zerodistance position on the abscissa axis of FIG. 3. The two curves of thisfigure show clearly that it is `desirable to have the transducer tippositioned as close -to the orifice plate as possible short of havingthis tip'poun'd or impact on the plate when the transducer is energized.In essence, it is desirable to create a piston pump having no head endclearance.

For the particular experiments providing the data of FIG. 4, thedistance from the transducer tip'to the orifice plate was kept at asingle value of about 0.00 in., that is, the value determined accordingto the data of FIG. `3 as that providing the greatest force and velocityof the air jet for a given orifice opening diameter. Force and velocitymeasurements were taken for a range of diameters of the orifice opening,and the two curves of FIG. 4 show clearly that there is a mid-rangeoptimum value of this diameter of about 01.050 in. Expressed as a rangeof ratios, it is desirable that the diameter of the transducer tip besix to fifteen times as great as the diameter of the orifice opening.More desirably, the former diameter y will be about ninetimes as greatas the latter.

V ered. The diameter of the orifice opening was kept at a single valueof about 0.040 in., and the distance from the transducer tip to theorifice plate was kept at a single value of about 0.00 in. Data gatheredin these experiments are given in Table I as follows:

These data show clearly that once a certain diameter of the transducertip has been reached, at least about 0.437 or TA6 in. for theexperiments described, no particular increase of either force orvelocity of the air jet will result from the use of a larger tip. On theother hand, if the tip diameter be reduced significantly below its lowerlimiting value for essentially constant air jet force and velocity therewill be a marked decrease in each of these two quantities.

Referring next to FIG. 5, experimental measurements have been made ofthe mass median drop diameters of water fed at various rates to anapparatus embodiment of this invention generally similar to that shownin FIG. 1, and atomized thereby. For these experiments the transducerhad a tip diameter of about 0.437 in., an operating frequency of about20 kc. p.s., and a variable power input. The diameter of the orificeopening was kept at a single value of about 0.040 in., and the distancefrom the transducer tip to the orifice plate was kept at a single valueof about 0.00 in.

For the atomized water, mass median particle sizes or drop diameterswere determined according to the method given in the article A Techniquefor the Investigation of Spray Characteristics of Constant Flow Nozzlesby I. H.

.Rupe appearing at pp. 680-694 of Third Symposium on Combustion, Flameand Explosion Phenomena, The Williams & Wilkins Co., 1949, Baltimore,Md. Essentially this method calls for atomized water to be collected ina series of cells filled with a material such as kerosene or StoddardSolvent. These materials are less dense than and immiseible with water.Therefore the water particles falling into the collection cells sink tothe bottom thereof while retaining their discrete identities, and maylater be viewed optically or photomicrographed for counting and sizing.

Velocities through the orifice opening of the air jets generated by thetransducer were not measured directly. Instead a force measurement ofthe transduceregenerated air stream was made according to the methodhereinbefore described for each power level of transducer operation.After that an air stream from a steady source of compressed air wasdirected through the same orifice opening used for the water atomizationexperiments, and force measurements were made of this stream, theeffective supply pressure at the stream source being adjusted through aseries of values to give such a measurement equal to each of those ofthe transducer-generated air stream. For each of these values ofsteady-source stream pressure, the volumetric flow rate of air issuingthrough the orifice opening was determined by means of a rotameter. Withknowledge of air flow rates and also of the diameter of the orificeopening, air velocity through this opening was calculated for eachsteady-source Vstream pressure value. These calculated values areindicated on the abscissa axis of FIG. as apparent air velocities. Theyrepresent, in effect, root means square velocity values of the air jetsgenerated by the transducer.

Water to be atomized was supplied or fed to the apparatus at fourdifferent rates, 0.01, 0.02, 0.05, and 0.275 gaL/hr. At each of the twolower rates of water feed, atomization was effected at a singletransducer power level'only. At each of the two higher rates,atomization was effected over a range of power levels. The plottedresults show that for a given level of transducer power,

region of the orifice plate.

this corresponding to a particular apparent -air velocity through theorifice opening, mass median drop diameter or particle size of theatomized water decreased steadily with decreasing rate of water feed.The plotted results show also that for a given rate of water feed themass median drop diameter decreased with increasing transducer powerlevel or apparent air velocity.

Referring next to FIG. 6, an orifice plate 87 has been substituted inthe apparatus of FIG. l for orifice plate 42 originally shown therein.Plate 87 is provided with a plurality of orifice openings in alignmentwith the head of bolt 24 on resonator element 22, that is, a pluralityof orifice openings closely adjacent the effective tip of transducer 20.Specifically, two orifice openings 88 and 90 are shown. It is within thecontemplation of this invention, however, that more than two openingsmay be provided in the orifice plate, and that they may be grouped inany suitable pattern such as a circle, a square, a diamond, etc.

The advantage Awhich accrues from using a plurality of orifice openingsrather than a single opening only is that of obtaining a better breakingup of the liquid feed stream trickling down the orifice plate from tube84. For a given total orifice area, a plurality of openings will havegreater total lip or edge length and surface than a single opening inway of the down-coming liquid for atomization. This additional lengthand surface will aid in dis tributing the liquid in the condition of athin, easily atomized film prior to going into the pulsating air jetsthrough the openings, and at least tend to increase the atomizingcapacity of the apparatus.

Although not illustrated specifically in any figure, it is within thecontemplation of this invention that orifice plate 42, orifice plate 87,or any other orifice plate be provided with a collar on its sideadjacent the transducer, this collar in fact enclosing the head of bolt24 or the tip of the transducer of whatever particular configuration. Asso disposed, the collar will act as the cylinder of a reciprocating airpump, and in some cases will tend to reduce side leakage of air drawn inthrough the orifice opening or openings on the suction stroke of thetransducer tip. This in turn will tend to allow the use of a tip ofsmaller diameter than if no collar were present for a given pumpingeffect. It is to be understood clearly, however, that the use of acollar or cylinder as described is not critical for successful operationof any apparatus embodiment of this invention.

Referring finally to FIG. 7, an orifice plate 92 is held horizontally bysuitable structural support means above .a vertically orientedtransducer 20 comprising a resonator element Z2 having a headed bolt 24'in its upper or tip end. Plate 92 has an upwardly lipped orifice opening94. A liquid feed tube 96 is disposed with its outlet end close to theupper side of the plate. When liquid material to be atomized is admittedonto plate 92 it will tend to form a little pool bounded by the lip ofopening 94 and the vertical portion of the outer rim or edge Continuedfeeding of liquid through tube 96 will cause overflow in thin Afilm formof the material to be atomized around the entire lip of the orificeopening, a desirable condition of operation.

Although this invention has been described with a certain degre ofparticularity, it is to `be understood that the A present disclosure hasbeen made only by way of example, especially with respect to numericalvalues given therein, and that numerous changes in the details ofelements and assemblies may be resorted to without departingfrom thespirit and scope of this invention asset forth in the following claimswhich are to be construed as broadly as the state of the relevant artallows.

What is claimed is:

1. An apparatus for atomizing liquids comprising (l) a transducercapable of receiving inputs of alternating voltage and providing outputsof vibratory mechanical displacement at a localized-surface region ofits structure,

9 and (2) an orifice-containing plate element disposed opposite saidregion, said plate and said region detining a very small clearance spacetherebetween such that at maximum displacement the area available forair flow between said region and said plate element is much less thanthe area of said orifice, whereby said Vibratory displacement of saidregion produces a pulsating air jet through said orifice capable offinely atomizing liquid at said orifice.

2. Apparatus according to claim 1 wherein the localized surface regionand the plate are essentially planar and parallel.

3. Apparatus according to claim 1 wherein the orifice is of diameterbetween about one-sixth and one-fifteenth that of the localized surfaceregion.

4. Apparatus according to claim 1 wherein the localized surface regionessentially is the Hat end of a piston which is vibrated in a directionsubstantially perpendicular to said fiat end.

5. Apparatus according to claim 1 wherein the transducer is operable atabout 20 kilocycles per second.

6. A method of atomizing liquids which comprises (l) vibrating at highfrequency a substantially plane surface region to displace said regionalong an axis substantially perpendicular thereto and towards and awayfrom an orifice in a plate element disposed closely adjacent to saidregion, the area of said orifice being much larger than the lateralclearance area lbetween said region and said element at maximumdisplacement of said region from said plate, whereby the vibration ofsaid region causes a jetlike pulsating air flow out of said orifice withrelatively very little lateral air flow between said region and saidplate element, and (2) flowing a liquid to be atomized to said orificewhereby said pulsating ow atomizes said liquid.

